Long-Term Grazing Intensity Research in the Missouri Coteau of North Dakota - 2012 Annual Report

Livestock Response

Table 4 shows the average daily gain, gain per acre, gain per ton of forage, and body condition scores from the different grazing intensities. Grazing pressure was too light on the heavy and extreme treatments in the first two years of the study, so no significant differences in average daily gains were observed in 1989 and 1990. Since 1990, average daily gain and animal body condition scores have decreased with increasing grazing intensity each year with few exceptions. The rate at which average daily gain decreases with an increase in stocking rate varies greatly from year to year. The differences between years may be due to variation in forage quality or quantity, the effect of weather on the animals, the animals’ initial weights, or their potential to gain.

Table 4. Average daily gains, gains per acre, gain per ton of forage and condition scores from different stocking intensities.

Desired Grazing Intensity

Average Daily Gains (lbs./head/day)

2008

2009

2010

2011

2012

Average 1991-2012

Light

1.75a1

2.05a

1.54

1.59

1.21a

1.39a

Moderate

1.58ab

1.99a

1.29

1.32

1.12a

1.27b

Heavy

1.35b

1.48b

1.09

1.30

0.98ab

1.11c

Extreme

0.95c

1.09b

1.02

1.17

0.72b

0.86d

LSD (0.05)

0.38

0.42

NS2

NS

0.34

0.12

Average Gain (lbs./acre)

2008

2009

2010

2011

2012

Average 1991-2012

Light

39.73b

47.37b

41.58

51.55c

36.81

31.31d

Moderate

68.61ab

90.63a

68.95

83.22bc

62.85

56.81c

Heavy

82.15a

92.72a

84.55

121.11ab

83.17

78.79b

Extreme

76.10a

90.79a

104.70

140.29a

80.16

89.26a

LSD (0.05)

29.04

34.31

NS

54.49

NS

9.60

Average Gain (lbs./ton of forage)

2008

2009

2010

2011

2012

Average 1991-2012

Light

27.11c

33.80b

19.01c

21.69b

17.88b

19.55d

Moderate

51.13b

62.10ab

31.24bc

32.82b

33.08ab

34.98c

Heavy

70.51ab

77.54a

52.54ab

58.61a

54.07a

58.95b

Extreme

78.22a

92.90a

64.87a

74.00a

58.94a

75.59a

LSD (0.05)

22.96

33.78

27.37

22.96

30.27

7.37

Condition Score

2008

2009

2010

2011

2012

Average 1994-2012

Light

6.99a

5.77

5.24

5.41

5.02a

5.45a

Moderate

6.51b

5.52

5.19

5.33

4.88a

5.33ab

Heavy

6.38b

5.46

5.16

5.42

4.78ab

5.22b

Extreme

5.82c

4.97

5.05

5.25

4.57b

4.96c

LSD (0.05)

0.39

NS

NS

NS

0.24

0.17

1Means in the same column followed by the same letter are not significantly different at p=0.05. 2Means not significantly different.

If all years are pooled together, the relationship between daily gain and stocking rate/acre has an R2 of 0.27, while the relationship between daily gain and stocking rate/ton of forage has an R2 of 0.33 which means that stocking rate explains 27 or 33% of the variation in average daily gain between pastures. When only one year is considered at a time, the R2 varies between 0.09 and 0.92 on a per acre basis and between 0.10 and 0.94 on a per ton of forage basis, with the 0.09 and 0.10 coming from 2007. The next lowest R2 was 2006, with R2s of 0.25 and 0.33, and third was 2011, with R2s of 0.30 and 0.32. Therefore, ignoring 2006 and 2007, between 30 and 94% of variation in average daily gain is a result of the difference in stocking rate. Forage production was well above average in 2007 and gains had not become forage-limited on the heavily grazed pastures by the time the cattle were removed. Forage production was well below average in 2006 and cattle were removed early, before the stocking rate had much opportunity to influence average daily gains (Tables 1 and 2, Figure 1. The relationships between stocking rate and average daily gain are illustrated in Figure 2. Reference lines indicate the average stocking rates for each of the four grazing treatments. Initially, gain/ton of forage increased as the stocking rate increased, but there comes a point when further increases in stocking rates result in reduced gain/ton (see Figure 3).

What happens at stocking rates beyond the extreme stocking rate reference line is mainly hypothetical because we have very few observations on which to base our regression lines. However, all but 2001, 2002, 2003, and 2007 had at least one observation from a stocking rate higher than the projected rate that would provide maximum gain/ton for the year. Table 5A shows the stocking rate that would have resulted in the maximum gain/ton of forage in each year. Since we cannot predict ahead of time which stocking rate will give the maximum gain/ton in a particular year, it would be impossible to stock each year for maximum gain/ton. In retrospect, if we were to pick one stocking rate that would have resulted in the maximum gain/ton from 1991-2012, it would be 2.49 AUM/ton. This is the point labeled optimum in Figure 3. Table 5B shows what the gain/ton would have been each year if we had stocked at that rate. We predict that if we had stocked at 2.49 AUM/ton each year, gain/ton would have ranged from a gain of 34.6 lbs./ton in 2006 to 150.5 lbs./ton in 1992 with an average of 76.6 lbs./ton. Table 5C shows what the gain/ton would have been each year if the stocking rate had been held constant at 0.70 AUM/ton, the average of the moderate treatment over this period.

Table 5. Comparison of gain in pounds per ton of forage from selected stocking rates.

A

B

C

Stocking rate in AUMs/ton of forage that would result in the maximum gain/ton in each year.

Stocking rate in AUMs/ton of forage that if held constant would result in the maximum gain/ton over the twenty two year period.

Gain/ton over the twenty two year period if stocking rate where held constant at 0.70 AUMs/ton of forage, the average of the moderate treatment over this period.

Year

AUMs/ton of forage

Gain/ton

AUMs/ton of forage

Gain/ton

AUMs/ton of forage

Gain/ton

1991

2.61

56.5

2.49

56.4

0.70

27.5

1992

3.84

171.9

2.49

150.5

0.70

56.6

1993

2.07

102.9

2.49

98.2

0.70

54.0

1994

1.83

40.1

2.49

35.1

0.70

25.2

1995

2.52

60.3

2.49

60.3

0.70

28.8

1996

2.52

58.7

2.49

58.7

0.70

26.6

1997

2.30

95.4

2.49

94.7

0.70

46.8

1998

2.10

75.6

2.49

72.9

0.70

40.3

1999

3.46

108.3

2.49

99.5

0.70

37.2

2000

2.75

70.9

2.49

70.3

0.70

30.5

2001

*

2.49

107.4

0.70

36.7

2002

*

2.49

106.1

0.70

39.0

2003

*

2.49

76.9

0.70

28.7

2004

1.50

80.1

2.49

34.9

0.70

49.7

2005

2.43

48.3

2.49

48.3

0.70

22.8

2006

3.08

35.9

2.49

34.6

0.70

15.3

2007

*

2.49

110.0

0.70

34.8

2008

1.89

80.4

2.49

71.7

0.70

46.2

2009

2.25

95.7

2.49

94.7

0.70

53.8

2010

1.85

65.6

2.49

57.0

0.70

37.9

2011

2.48

82.5

2.49

82.4

0.70

38.4

2012

2.35

64.1

2.49

63.9

0.70

30.4

22-year avg.

2.43

77.4

2.49

76.6

0.70

36.7

* The regressions for 2001, 2002, 2003 and 2007 were not suitable to project the peak in gain/ton.

Figure 4 shows the relationship between stocking rate and economic return. Costs for land, labor, and management are not included because these values vary greatly from one operation to another. If cattle prices were steady, then return/ton would peak at a stocking rate somewhere below maximum gain/ton, with the exact point depending on carrying costs (interest, death loss, salt and mineral cost, veterinary cost, transportation, labor, and land). However, when cattle are worth more per hundredweight in the spring than they are in the fall, the point of maximum return/ton occurs at a lower stocking rate. When the cattle are worth more in the fall, the maximum return/ton occurs at a higher stocking rate. Again, returns for stocking rates beyond the extreme stocking rate reference line are hypothetical and all but 1992, 2001, 2003, 2006 and 2007 had at least one observation from a stocking rate higher than the rate that would provide maximum return to land, labor, and management for the year. Table 6 shows what the optimum return/ton would have been for each year if stocking rate were set for the optimum for that year (A), if the stocking rate were held at a constant optimum rate (B), or if the stocking rate were held constant at the moderate stocking rate (C). The peaks of the curves in Figure 4 correspond to these optimum stocking rates. If we were to pick one constant stocking rate that would have provided the maximum return/ton over the last 22 years, it would be 1.86 AUM/ton. This is the point labeled "optimum" in Figure 4. In 2010, cattle prices were higher in the spring than in the fall for cattle weighing less than 875 lbs. This coupled with the lower rate of gain of cattle on the higher stocking rates would put the maximum return for 2010 at $9.67/ton if stocked at 0.90 AUM/ton. Last year (2011), cattle prices were higher in the fall than in the spring for cattle weighing more than 500 lbs. This plus the highest forage production in of the twenty-four years put the maximum return for 2011 at $60.81/ton if stocked at 2.39 AUM/ton. Again this year (2012), cattle prices were higher in the spring than in the fall for cattle weighing less than 875 lbs. This coupled with the lower rate of gain of cattle on the higher stocking rates would put the maximum return for 2012 at $15.92/ton if stocked at 1.25 AUM/ton. Although the average return/ton is higher under the optimum stocking rate, there were six years with negative returns, while only one year had a negative return under the moderate stocking rate. (Costs for land, labor, and management have not been subtracted). If you compare Tables 5 and 6 you can see that the stocking rate with the greatest economic return was less than the rate with the greatest gain per ton of forage in all but three years (1996, 1999 and 2004).